CC112X/CC1175
SWRU295C
Page 17 of 108
0
1
2
3
4
5
6
7
8
9
10
126 127
x
x
RXFIRST
RXLAST
NUM_RXBYTES = 0x00
x
x
x
x
x
x
x
x
x
x
x
transmitted on the air and received by
the radio
3
D
0
D
1
D
2
0
1
2
3
4
5
6
7
8
9
10
126 127
x
x
RXFIRST
RXLAST
NUM_RXBYTES = 0x04
x
x
x
x
x
x
x
x
D
0
D
1
D
2
transmitted on the air and received by
the radio
3
D
0
D
1
D
2
0
1
2
3
4
5
6
7
8
9
10
126 127
x
x
RXFIRST
RXLAST
x
x
x
x
D
0
D
1
D
2
NUM_RXBYTES = 0x08
3
D
0
D
1
D
2
Figure 7: FIFO Pointers (RX FIFO) (1)
If 8 bytes (
NUM_RXBYTES = 0x08
) are read from the RXFIFO using standard FIFO access (see
Section 3.2.4) the following will be read: 3, D
0
, D
1
, D
2
, 3, D
0
, D
1
, D
2
.
If the RX FIFO had been read (using standard FIFO access) in between the two packets, the RX
FIFO pointers would end up with the values shown in Figure 8.
0
1
2
3
4
5
6
7
8
9
10
126 127
x
x
RXFIRST
RXLAST
x
x
x
x
D
0
D
1
D
2
NUM_RXBYTES = 0x04
D
0
D
1
D
2
x
Figure 8: FIFO Pointers (RX FIFO) (2)
3.2.4
Standard FIFO Access
Using the standard FIFO push/pop interface the 128-byte TX FIFO and the 128-byte RX FIFO are
accessed through the 0x3F address. When the R/W
¯ bit is zero the TX FIFO is accessed, and the RX
FIFO is accessed when the R/W
¯ bit is one. Using this type of access, the TX FIFO is write-only, while
the RX FIFO is read-only. The burst bit is used to determine if the FIFO access is a single byte access
or a burst access. The single byte access method expects a header byte with the burst bit set to zero
and one data byte. After the data byte, a new header byte is expected; hence CSn can remain low.
The burst access method expects one header byte and then consecutive data bytes until terminating
the access by setting CSn high.